The referenced U.S. Pat. No. 5,142,191, Blaisdell et al., describes a icy-pressure discharge lamp and, specifically, a subminiature fluorescent lamp which has end terminals formed by press seals for accurate alignment of the lamp relative to an optical system.
The discharge vessel of the low-pressure discharge lamp, hereinafter, for short and generically, a fluorescent lamp, is hermetically closed off at both ends. This hermetic seal can take on two forms, namely either a pinch or press seal or a flare mount, sealed to the ends of the tubular discharge vessel. Two current supply leads at both ends of the tubular discharge vessel are placed in the plane of the pinch or press seal or, respectively, the press portions of the flare mounts, and are carried beyond these seals, outwardly thereof. The leads are melt-sealed to be gas-tight.
Bases which have sleeve portions can be placed over the ends of the tubular discharge vessel for engagement in suitable sockets. The base sleeves are identical at both ends of the discharge vessel and, at a free end, have an essentially plate-like portion, projecting from the sleeve portion of the bases and set on edge, to form, in cross section, approximately a rectangle. This free end portion, which can be snapped between spring terminals in the socket, has oppositely located plane side walls, extending essentially parallel to the plane of the pinch or press seal, or the press portion of the flare mount. The plate-like portions are perforated, that is, formed with openings extending from the facing end, to receive the terminal leads from the electrode connections of the lamp. These terminal leads are bent over the face of the plate element in opposite directions, and then back towards the discharge vessel, parallel to the axis of the lamp. The contact wires, then, will be positioned at respective opposite sides of the plate-like extension, in engagement with the flat or plane side walls thereof.
If the seals at the two ends of the tubular lamp are not in alignment with respect to each other, for example have some twist, or if the bases at the respective ends of the lamp are not placed in exact alignment, the orientation of the plate-like extension of one base will likewise be misaligned with the plate-like extension of the other base. This, then, will also result in relative twist or misalignment of the contact ware pairs at the opposite ends of the discharge vessel, with respect to each other.
The angle of this twist or misalignment depends on the error in aligning the pinch seals or the melt connection of the flare mount in manufacture from perfect alignment. It is very expensive to obtain accuracy in alignment of the seal at the two ends of such a lamp. During mass production manufacture, some tolerance should be permissible. A maximum relative twist angle of about 5.degree. can be maintained with suitable economics of manufacture. As the requirement for accuracy in alignment increases, costs of manufacture also increase.
The sockets for the fluorescent lamps to which the present invention relates customarily use two flat leaf spring terminals, or resilient segments, positioned in the approximate spacing of the two plane side walls of the end plate of the bases of the lamp, and located parallel with respect to each other. Electrical contact between the base and the socket is obtained by direct contact between the contact wires adjacent the planar size surfaces of the base with the leaf spring terminals in the socket.
If the twist angle of the two bases on the lamp with respect to each other exceeds a certain tolerance angle, which depends largely on the diameter of the contact wires, the edges of the base end portion located in the direction of the longitudinal axis of the discharge vessel have the tendency to spread the leaf spring contacts of the sockets outwardly. This interferes with reliable electrical connection and may even interrupt electrical connection between the base and the socket. The shape or form of the narrow walls of the plate-like extension need not be flat; it may be curved, so that no right angles result between the side walls of the end portion of the base and the narrow side walls thereof.
Increasing the diameter of the connecting wire to the electrode to obtain reliable terminals even with a maximum permissible tolerance misalignment angle beyond customary wire diameters is not readily possible because the melt seals to the wires, that is, for example the press seal at the end of the tubular discharge vessel, or the wire seal through a flare mount, may become leaky, leading to destruction of the lamp.